Feature association in image analysis

ABSTRACT

Methods and apparatus are described by which detected signal pulses arising from features in a field can be associated to thereby generate so-called agglomerates of features, in dependence on the relative spacing of the features in the field. In this way it is possible to link up the detected signal pulse information relating to small features arranged approximately in straight lines. The invention generates capture zones from each feature one extending in the line scan direction and the other generally perpendicular thereto. The invention envisages the combination therewith of an associated parameter computer whereby information may be obtained relative to a parameter of each detected feature. The information from features within an agglomerate may be suppressed or collated and released as a single information signal relating to the agglomerate. Thus where a count pulse is generated for each feature these may be inhibited from all features within an agglomerate and the latter counted as a single feature. Alternatively where a signal proportional to the area of each feature is generated by the associated parameter computer, these may be combined for features within an agglomerate and a total area signal released for the agglomerate proportional to the total of the individual areas of the features within the agglomerate.

United States Patent [191 Gibbons et al. p a

[ FEATURE ASSOCIATION IN IMAGE ANALYSIS [76] Inventors: John MichaelGibbons, The Grange;

William Ralph Knowies, 40 Flambauls Cir., both of Meldreth, Royston,England [22] Filed: May 8, 1972 [21] Appl. No.: 251,495

[30] Foreign Application Priority Data May 6, l97l Great Britain13590/71 [52] US. Cl. 235/92 PC [51] Int. Cl. G06m 11/04 [58] Field ofSearch 178/6, 6.8, 7.], 7.2, DIG. 37, l78/DIG. 36, DIG. l; 235/92 DN, 92PB, 92

[56] References Cited UNITED STATES PATENTS I 2,89l,722 6/1959 Nuttallet al l78/DlG. 36 3,020,033 2/1962 McCreanor et al. l78/DIG. 373,280,692 10/1966 Milnes et al. i. l78/DIG. 1

Primary Examiner-Robert L. Griffin Assistant ExaminerGeorge G. StellarAttorney, Agent, or FirmOblon, Fisher, Spivak, Mc- Clelland & MaierMai-,5, 1974 [5 7] ABSTRACT Methods and apparatus are described by whichdetected signal pulses arising from features in a field can beassociated to thereby generate so-called agglomerates of features, independence on the relative spacing of the features in the field. In thisway it is possible to link up the detected signal pulse informationrelating to small features arranged approximately in straight lines.

The invention generates capture zones from each feature one extending inthe line scan direction and the other generally perpendicular thereto,

The invention envisages the combination therewith of an associatedparameter computer whereby information maybe obtained relative to aparameter of each detected feature. The information from features withinan agglomerate may be suppressed or collated and released as a singleinformation signal relating to the agglomerate. Thus where a count pulseis generated for each feature these may be inhibited from all featureswithin an agglomerate and the latter counted as a single feature.Alternatively where a signal proportional to the area of each feature isgenerated by the associated parameter computer,

these may .be combined for features within an.

agglomerate and a total area signal released for the agglomerateproportional to the total of the individual areas of the features withinthe agglomerate 25 Claims, 12 Drawing Figures PATENTEDHAR 519143,795,792

SHEET 1 0F 5 0 STRETCH DETECT a "0am V AC? nmcToR-''" Fig 3 Fig APATENTED 51974 3.795.792 SHEET 2 0F 5 'v| SIGNAL T0 CONTROL 58MONOSTABLE DURATION TRAILING START EDGE DETECTOR y DETECTOR MONOSTABLE0/P STOP DURATION WI V 62 52 on f 132 A AC? SET Q DETECTOR BISTABLEDELAY T I08 mggsz DATA CLEAR sToR'E STORE A 0R To HOLD DATA 1 /HO ||4 NoYES DELAY LINE 1 t ggg COMPARE HEIGHT DATA '6 "T" ZERO "mm DATA ENABLESUBTRACTION OF I.

PATENTEDMAR 51914 3.795.792

SHEET 3 OF 5 I 7 I] I 64 66 I, g l x172 l a I if!) 9211/ w 12 J 0/ l0 Esi lze" PATENTEDHAR 5W 3,795,792

S'zitU h 0F 5 us I52 :04

AP COMPUTOR n V w ACP DETECTOR Acry PATENTED MAR 51974 SHEET 5 [If 5 vsIGNAL To CONTROL 58 MONOST BLE DURATION ,54 60 56 TRAILING STARTDETECTOR EDGE v DE-TEGTDR MONOSTABLE 0/P 5T0 DURATION WI. T ,50 Q 2 on52 F I32 l34 l36 l Ac P sET Q DETECTOR DELAY 70/ RESET BISTABLE BISTABLE86 /az 80 TRAILING 9 L- wz EDGE 78 Q DETECTOR W2 ISQ 24 RELEASE DATACLEAR sToRE STORE TO HOLD DATA I I ll4 NO YES /l SUBTRACT DELAY LINE IFROM COMPARE -w2 HEIGHT DATA HEIGHT DATA "6 TRANSMIT INTo RECIRCULATESUBTRACT'ON OF HOLD I I '42 AP AREA AP 26%; n- I40 DETECTOR AACP(RELEASE AP ouT) FEATURE ASSOCIATION IN IMAGE ANALYSIS This inventionconcerns methods and apparatus for analysing features in a field inwhich a video signal thereof is generated by line scanning the amplitudeexcursions relating to feature content are detected by comparison withone or more reference voltages and measurements are made on the detectedsignal pulses. In particular the invention concerns a method andapparatus by which information relating to features and obtained by anassociated parameter computer of the type described in U.S. Pat. No.3,619,494 is not released at the end of scanning a feature if anotherfeature is detected as being within a given proximity of the firstfeature, but is witheld and released for the agglomerate i.e., set, offeatures as a single associated parameter therefor.

The information signal may for example be a count pulse and it may bedesirable to inhibit the count pulse for each of a set of features allwithin a given distance from each other and to release only that for thelast feature in the agglomerate. The action of associating features independence on their proximity will be referred the line scan direction,by the time taken to scan the given distance. If their spacing is lessthan this distance, the detected signal pulses of the second featurewill overlap with the stretched ones from the first and the twoinformations can be combined.

The present invention allows link up of information in a directionperpendicular to the line scan direction as well as parallel thereto.

According to the present invention, each line scan intersect pulse in adetected video signal is stretched by a predetermined amount to form amodified pulse, at least one signal relating to the last modified pulsefor each feature is recirculated from line to line, coincidence betweena modified pulse of one feature and that of an adjacent feature in thefield is detected and a warning signal generated if coincidence occurs.Conveniently the warning signal uniquely identified information obtainedfrom scanning each such feature.

Thus, for example, information may only be released for features in anagglomerate or only features not in an agglomerate or only one signalreleased after the last feature in an agglomerate has been scanned.

The information signal may for example represent the accumulation of allthe information signals obtained from all the features in theagglomerate e.g. their total area. The areas of the stretch regions mayalso be included.

Alternatively. where the information signal for each feature is a countpulse each may be inhibited for each feature in an agglomerate and onlyone count pulse regenerated). Or alternatively the size of the box maybe made dependent on a dimension such as the area, height or width ofthe feature.

Thus, for example, the said predetermined number of line scans may bedetermined'from a parameter of the feature such as its length measuredin a direction perpendicular to the line scan direction, so that theheight of the capture zone is made dependent on the feature height.

The recirculation of the signal defining the box. zone may occur atprecisely one line scan period intervals, in which case the capture zonegenerated by the recirculating pulses will have sides which'areperpendicular to the line scan direction.

If, however, the recirculation period is made less than or greater thanone line scan period, the sides of the capture zone will be inclined tothe line scan direction.

Preferably means are provided for inhibiting the recirculation of thesignal defining a box zone for one feature if that signal coincides witha detected signal pulse relating to another feature or a stretchedportion of a detected signal pulse relating to another feature, so thatonly one box zone exists for one agglomerate at any instant.

Alternatively, where coincidence of the recirculating signal defining abox zone and the stretched portion of a detected signal pulse, isdetected and it is not possible to slip the information in theassociated parameter computer by a sufficient amount against thedirection of line scan so as to follow the trailing edge of the stretchzone of the new capture zone, the trailing edge of the first box zone,(and thereby the information associated therewith) is caused to slipforward against the line scan direction by a controlled amount on eachline scan, until the position'of the trailing edge of the new capturezone is reached or until the stretch zone thereof terminates.

The invention will now be described by way of example with reference tothe accompanying drawings, in which:

FIG. 1 illustrates a field containing an agglomerate which is counted asa single feature by,a first embodiment of the invention,

FIG. 2 illustrates separate feature counting,

FIG. 3 is a block circuit diagram of a first embodiment of theinvention,

FIG. 4- illustrates non-metallic inclusions in steel,

FIG. 5 is a block circuit diagram of a further embodiment, I

FIGS. 5a 5d illustrate the capture zones generated by the circuit ofFIG. 5,

FIG. 6 is a block circuit diagram of a modification of the furtherembodiment of the invention,

FIG. 7 is a block circuit diagram of an ancillary AP computer,.and iFIG. 7a illustrates the operation of the computer of FIG. 7. I

In FIG. 1 features 10 are so close as to fall within the individualcapture zones formed by the present invention, whilst feature 12 beingisolated does not link up with any other feature in the field. Thefeatures 10 form an agglomerate and'only a single count pulse isproduced for the agglomerate shown at 14. The usual count pulse 16 forthe feature 12 is released at the end of its capture zone 15.

In FIG. 2, each feature is shown as being counted separately byproducing a single count pulse at the end of scanning each feature.

In FIG. 3, an analogue video signal at 18 (e.g. from a television camera(not shown)) is supplied to a threshold detector 20 which produces abinary type detected signal having a l-value when the video signalamplitude exceeds the detection threshold voltage V1 and a -value atother times. This detected signal appears at 22.

The l-value pulses so obtained are sometimes referred to as line scanintersect pulses. I

In order to provide a simple measure of their duration and also toenable the overall system to be synchronized, the intersect pulse signalat 22 is sampled at regular intervals and the 1- or 0- value obtainingat the sampling point is maintained for the remainder of the intervalprior to the next sampling. The signal is then said to be clocked. Thesampling points along each line scan are called picture points and thetime taken to scan between 2 adjacent picture points is a picture pointinterval.

Each intersect pulse is stretched by the addition of a pulse of npicture point intervals, by a stretch circuit 24, to produce modifiedpulses at 26.

The signal at 26 provides an input to a one line delay device 30 (whichis preferably a shift register) via an OR gate 28. The other input forthe gate 28 is derived from point 32 at the output of the delay 30.

The signal at 32 is prevented from passing to point 36 by gate 34 whichis only opened during the last line scan in the frame. Counter 38generates a single count pulse from each modified pulse from point 32during this last line scan and counts each generated count pulse. Thecount pulses are conveniently generated by detecting the trailing edgeof each modified pulse by a differentiating and rectifying circuit asemployed in the counter described in US. Pat. No. 3,619,494.

A separate counter is provided for counting every feature as in FIG. 2.To this end the signals at 22 are supplied to a circuit 40 for detectingthe last intersect pulse for each feature (i.e., an ACP counter) andgenerating a single count pulse for each feature at the anticoincidencepoint (ACP) for the feature. These pulses appear at junction 42 and arecounted by counter 44 set to count all such pulses during a single framescan. One form of ACP counter is described in US. Pat. No.

The invention is primarily applicable to the assessment of non-metallicinclusions in a steel sample, where the video signal is obtained from atelevision camera which views the polished steel sample through amicroscope. Suitable choice of threshold voltage allows a detectedsignal to be produced in which the pulses only relate to oxideinclusions.

Some types of oxide inclusion are distributed randomly over the metalsurface area. Other types occupy narrow zones running parallel to therolling direction employed in the manufacture of the steel. This rollingaction breaks up a large oxide inclusion into a number of smallinclusions which are separated and spread along the rolling direction.Such a group of oxides is known as a stringer and one is shown at 46 inFIG. 4.

Other isolated inclusions, not forming a stringer are shown at 48.

By counting all the detectable oxide regions (i.e.,disregarding whetherthey are contained in stringers or otherwise) a total inclusion count isobtained and a comparison of the total oxide count and the number ofoxide regions when account is taken of the stringers (i.e., theinclusions within a stringer are all counted as one) gives a measure ofthe proportion of features that are within stringers.

FIG. 5 is a block circuit diagram of a further embo'diment of theinvention in which provision is made for adjusting the size of thecapture zones. A first size adjustment is provided by an adjustablestretch'producing circuit and a second size adjustment is provided by acontrol over the number of times the signal is recirculated to generatea box zone beneath a stretch zone of the capture area.

A video signal is generated by a television camera 50 coupled to a lightmicroscope 52 and video signal amplitude excursions relating to desiredfeature content are isolated from the remainder of the video signal by adetector 54 in which the video signal amplitude excursions are comparedwith a reference voltage V1 and detected signal pulses are generated forthe duration of each excursion which exceeds the reference voltage. Atrailing edge detector 58 generates a start signal for a monostabledevice 60 from the trailing edge of each detected signal pulse. A resetor stop signal for the monostable device 60 is also obtained fromjunction 56 direct. Thus, at the beginning of a detected signal pulse,the monostable 60 is reset irrespective of its initial condition and isrestarted as soon as the trailing edge of the pulse is detected.

The output from the monostable 60 is applied to one I input of OR-gate62 the other input being derived from junction 56. The output fromOR-gate 62 therefore comprises detected signal pulses each of which isstretched by WI. The output from OR-gate 62 thereby defines the originalfeature 64 (see FIG. 5a) of which the trailing edge is shown in dottedoutline together with a stretch zone 66 formed by the monostable outputpulses attached to the trailing edge of each detected signal pulse fromjunction 56. The detected signal pulses which therefore appear atjunction 68 are referred to as modified pulses and can be thought of asrelating to a feature formed by the two regions 64 and 66.

' The anti-coincidence point for the feature so defined is detected byan ACP detector 70 of the type described in US. Pat. No. 3,619,494 inwhich junction 10 corresponds to junction 68 in FIG. 5 hereof. The ACPis illustrated in FIG. Ed at 72 and the signal generated at point 72 issupplied via OR-gate 74 to set a bistable device 76. The set outputsignal from bistable 76 is supplied to junction and this signal isdelayed by a delay device 78 by a time interval W2 ro provide a resetsignal for bistable 76 a time interval W2'after the bistable device 76is set. The pulses at junction 80 are applied to a delay device 82 ofdelay equal to L minus W2 where L is equal to one line scan period. Theleading edge of each delayed signal thus appears a timeinterval W2 inadvance of the position of the ACP 72 (in FIG. 5a) on the next line scanand the trailing edge of the delayed pulse at 84 thus coincides (on thenextline scan) with the position of the ACP 72. This trailing edge isdetected by trailing'edge detector 86 and the short signal indicatingthe end of a pulse appears at junction 88 and is applied via gates 90and 92 as a second input to OR-gate 74 thereby setting bistable 76 atthe same point on the next line scan as it was set by the ACP at 72 onthe previous line scan. So far it is assumed that zero signal obtainedat junctions 94 and 96 so that an enabling signal is provided at theoutputs of amplifiers 98 and 100 respectively thereby enabling gates 90and 92.

The setting of bistable 76 on each successive line scan defines a boxzone 102 (see FIG. 5a) the width of which (i.e. measured in the linescan direction) is determined by the duration W2 and the height thereof(i.e. measured perpendicular to the direction of line scan) isdetermined by a height data signal supplied from junction 104 as oneinput to an AND-gate 106 having the ACP signal from ACP detector 70supplied to its other input. The height data from junction 104 isapplied via OR-gate 108 to a delay line 110 having the same delay (Lminus W2) as delay 82so that the height data is available at junction112 at the same time on the next line scan after the appearance of anACP 72 as is the set signal for bistable 76. The height data at junction112 is transferred to a subtraction stage 114 to which an enable signalis supplied after complete transfer of the height data, the action of114 being to subtract one from the numerical height data suppliedthereto. The reduced height data appears at junction 1 16 and this iscompared in comparator 118 with a zero and a no signal generated if thereduced height information does not equal zero which serves as a holdsignal for a store 120 to the input of which the reduced height data issupplied from junction 116.

The reduced height data stored in 120 is released therefrom by theappearance of a signal at junction 122 i.e. by the signal indicating thetrailing edge of the pulse of duration W2 from junction 84 on that linescan. The reduced information from store 120 is applied via OR- gate 108to the input of delay line 110 for recirculation and the process iscontinued until the reduced height data appearing at junction 116 equalszeroat which time the no"'signal is not generated and instead a stretchregion 66 is merged with the detected signal pulse arising from scanningfeature 64' on the same line scan and a fresh ACP 72 is detected for thenew stretch zone 66. A box zone 102 is generated therefrom in the samemanner as described hereinbefore.

Referring now to FIG. 5c, if a box zone 102 intersects a second feature64", a detected signal pulse will appear at junction 56 and thereforevia OR-gate 62 at junction 68 sometime during the duration of a delayedpulse at junction 84. In this event both inputs of AND- gate 132 aresatisfied and a set signal is provided for a further bistable device 134the set output of which is delayed by a short delay device 136 (toprevent a socalled race) thereby producing a signal at junction 94 andcausing gate 90 to be inhibited. The trailing edge signal for that pulseat junction 84 is therefore prevented from circulating via gates 90 and92 to again set bistable 76 and box 102 is therefore stopped at thatparticular line scan. Coincidence of signal at junction 94 and thetrailing edge signal at junction 88 satisfies both input condition for afurther AND-gate 138 the output of which is arranged to clear any signaltemporarily stored in store 120. This removes height data which iscurrently being recirculated for box 102 and thereby clears the countdown circuit as far as box 102 is concerned.

In this way the box zone generating circuit and box height controllingcircuit are both inhibited and the detected signal pulses relating tofeature 64" together with the pulses in the output of monostable 60relating thereto define a new stretch zone 66" for which a fresh boxzone 102" is generated as before described. No agglomerate ACP signalpulse is generated with relation to box zone 102 and providing that boxzone 102" does not intersect another feature, the agglomerate ACP signalpulse at the end of box 102" willappear as-a single yes signal isgenerated which appears at junction 96.

This provides an input for phase inverting amplifier 100 therebyremoving the signal on the second input of gate 92 and inhibiting thecirculation of the trailing edge signal from gate 90 to gate 74. Thisprevents bistable 76 being set and the box zone 102 is therebydiscontinued.

A signal indicating the end of the box zone 102 is generated by anAND-gate 124 one input of which is supplied with signal from junction 96and the other from junction 126 in the output of gate 90. Thus thetrailing-edge pulse from junction 88 which appears in the output of gate90, when coincident with a yes signal from comparator 118, causes bothinputs of gate 124 to be satisfied and a short duration pulse isgenerated known as the agglomerate ACP illustrated at 128 in FIG. 5a. Apulse counter 130 is set to count the agglomerate ACP signals such as128 which are generated during a complete frame scan.

.In the event that a second feature 64' lies within the stretch zone 66of feature 64 (see FIG. 5b) the leading edge of each detected signalpulse from feature 64' causes the monostable 60 to be reset or stoppedand the trailing edge thereof causes it to be restarted so that a freshstretch zone 66' is generated from the trailing edge of feature 64'. NoACP is produced from the original stretch zone 66 since the stretchedpulse which would have produced the ACP from feature 64 and count pulsefor the two features 64 and 64". I

In FIG. 5d the alternative intersection condition is shown in which astretch zone 66" from a feature 64" intersects the box zone 102 fromfeature 64. This con- .dition is again detected by'coincidence of signalat junction 68 and signal at junction 84 producing a set condition ofbistable 134 which is delayed by delay 136 and causes an inhibit signalfor gate thereby preventing the continuation of box 102 as beforedescribed. The trailing edge signal at junction 88 provides the resetfor bistable 134 and also serves to clear the height data stored instore as before described so that the circuitry is ready to generate anew box zone 102" after the ACP 72" is detected for stretch zone 66'. Ifnew box zone 102" doesnot intersect a further feature the signalappearing at ACP 128" constitutes a single count pulsefor the twofeatures 64 and The total count in counter at the end of a completeframe scan will equal the number of agglomerates detected. This countcan be compared with that obtained using an ACP detector 40 and counter44 as described with reference to FIG. 3 and supplied with the detectedsignal pulses from junction 56 of FIG. 5. The. comparison of the twocounts will indicate the proportion of features in agglomerate to thosenot in agglomerat'es.

FIG. 6 is based on FIG. 5 and to a large extent is identical thereto. Tothis end the same reference numerals havebeen used to describe similarparts thereof and only those parts which differ from FIG. will bedescribed. v

The object of the modifications contained in FIG. 6 is to allow a signalto be generated corresponding to the total area of all featurescontained in an agglomerate and to allow this signal to be released asan associated parameter for the agglomerate. It is to be understood thatalthough the parameter which is measured is the area of the featureswithin the agglomerate, the same principle may be employed for any otherparameter which can be obtained by measurements made on the detectedsignal pulses arising from scanning features in a field.

The area of each feature is measured by supplying the detected signalpulses from junction 56 as an input to an associated parameter computer140 of the type described in our British Pat. Specification No.1,264,805. Junction 56 of FIG. 6 corresponds to junction 10 of FIG. 2 ofthe drawings accompanying the aforementioned British PatentSpecification.

The AP computer 140 comprises a first computing device (not shown) towhich the detected signal pulses from junction 56 are supplied and whichis adapted to generate for each detected signal pulse an electricalsignal of magnitude corresponding to the duration of the pulse. Eachsuch generated signal is supplied via an delay device (not shown) isalso supplied to the accu-.

mulator so that signals from the delay device (not shown) which arisesduring a detected signal pulse at junction 56 or during the stretch zoneassociated therewith are added to form a new value for circulation viathe delay line to the next line scan. To this end a further trailingedge detector 142 is provided the input of which is supplied fromjunction 144 in the output of monostable 60 and the output of trailingedge detector 142 provides one input for an OR-gate146 the other inputof which is provided by the signals appearing in the output of trailingedge detector 86 at junction 88.

It will be seen with reference to FIGS. 5a to 5d that no pulse iscirculated on theline containing an ACP such as 72 and there will be notrailing edge detected by trailing edge detector 86 or 142 on the linescan intermediate the stretch zone 66 and box zone 102. In consequenceno recirculate information would be applied to the AP computer 140 onthe line scan containing an ACP and the information would be lost unlesssteps were taken to ensure that a recirculate command signal was alsosupplied to the AP computer 140 on the intermediate line scan containingthe ACP 72. To this end the output from ACP detector 70 is also suppliedto a third input or OR-gate 146 so that on the line scan immediatelybelow the stretch zone 66 the information in the accumulator of the APcomputer is transmitted into the delay device at the ACP 72. Where theAP computer 140 requires a signal indicating the end of each actualdetected signal pulse the output from trailingedge detector 58 can besupplied thereto. This may be required in the event that the firstcomputing device requires to be reset at the end of each detected signalpulse supplied thereto and a signal is required to transmit the pulseduration signal from the first computer means into the accumulator.

The signal from AND-gate 124 previously describes quently theagglomerate ACP signal is shown applied to AP computer and this signalserves to release the information from the delay device (not shown) andinhibit the further recirculation of this information via theaccumulator thereby clearing the computer store. The information whichis gated out in this way constitutes the signal indicative of the totalarea of the features within the agglomerate and this is designated bythe arrow AP out.

It will be seen that the information signal relating to the area offeatures so far agglomerated will always be available at the trailingedge of either a stretch zone or a box zone and since the increment ofarea information arising from the detected signal pulse of a featurewill have been transmitted into the accumulator at the end of thedetected signal pulse which will always occur prior to the end of thestretch zone pulse associated therewith, the value in the accumulator atthe end of the stretch zone pulse will always be the correct value forcirculation into the delay device.

By providing a delay device in the AP computer 140 which is less thanone line scan period by a W2 (i.e., it corresponds to the delay device82) the area information delayed from the previous line scan is alwaysavailable at the beginning of the box zone 102 and is thereforeavailable for transmission into the delay device prior to the end of thebox zone in the event that a feature link-up occurs such as illustratedin FIG. 5d. To this end the output from the shortened delay device issupplied to the accumulator and is held therein until a recirculatesignalis obtained from OR-gate 146.

FIG. 7 illustrates how separate height information may be obtained foreach feature in the field depending on some parameter of the feature. Tothis end the detected signal pulses from junction 56 are supplied to afurther AP computer 148 controlled by its. own ACP detector 150 alsosupplied with the detected signal pulses from junction 56. The APcomputer and ACP detector 148 and 150 respectively may be of the typedescribed in British Pat. Specification No. 1,264,805 and the signalindicating the measured parameter for the feature is released by a gate152 operated by the ACP pulse from the ACP detector 150 in the mannerdescribed in the aforementioned British Patent Specification. Theposition of the released information is shown at point 154 in FIG. 7aand it will be seen that this occurs time W1 in advance of the ACP forthe stretch zone 66. Consequently the released information in FIG. 7 isdelayed by a delay device 156 of delay equal to W1 (which equals thereset time for monostable 60) and the output from the delay device 156is supplied to junction 104. In the event that an ACP signal appearsatpoint 72 (i.e. the stretch zone 66 does not intersect any other feature)the ACP detector 70 provides a pulse at point 72 and the delay device156 provides the height data signal at junction 104 and both inputconditions for AND-gate 106 are'satisfied. In-the event that no ACPpulse appears at point 72 for feature 64 (i.e., stretch zone 66 hasintersected another feature (not shown)in FIG. 7a) no ACP signal willappear at point 72 in the scan raster and the height date relating tothe first feature in the agglomerate and appearing at junction 104 willnot be passed by AND-gate 106.

The AP computer 148 may be set to measure the area of the feature and torelease a signal proportional to the area so that the height informationsupplied to junction 104 increases with the area of the feature therebyincreasing the height of the box zone for larger featuresv An invertingamplifier may be provided so as to reduce the size of the signalsupplied to junction 104 for increasing area thereby producing smallerboxes for larger features. Alternatively the AP computer 148 may be setto measure thelength dimension of the feature 64 (FIG. 7a) in adirection parallel to or perpendicular to the line scan direction or anyother direction and the information supplied to junction 104 is madedependent on the value of the length dimension so measured.Alternatively the perimeter of the feature 64 may be measured and theheight data supplied to junction 104 modified according to the perimeterof the feature last detected.

So far the width of the box zone (i.e., the length dimension of the boxzone measured in a direction parallel to the direction of line scanning)has been assumed to remain constant and the box zone so generatedtherefore has parallel sides which are perpendicular to the line scandirection in view of the relationship between the delay device 82 andthe duration of the pulses at junction 80. If however the delay device82 is made a small fraction of a line scan period less than or greaterthan L minus W2, then the box zone will become a parallelogram havingtop and bottom edges parallel to the line scan direction but sides whichare inclined to the line scan direction by an angle not equal to 90. Inthe event that delay device 82 is made different from L minus W2 delaydevices 110 and any delay device employed in AP computer 140 or APcomputer 148 must be made equal to the delay introduced by the modifieddelay device 82.

A further modification may be made whereby the value of W2 may be madeless during each successive line scan during which a box zone isgenerated and the delay introduced by delay device 82 increased ordecreased by a corresponding amount so as to generate a box zone oftrapezoidal or triangular shape. Any changes in the value of W2 and thedelay introduced by delay device 82 during successive line scans of abox zone must of course be duplicated in delay device 110 and thedelay'device in AP computer 140 and 148 if employed. i I

Since the recirculating count value in delay device 110 is reduced byone for each line scan of a box zone, this recirculating signal may beemployed or at least sensed and a signal generated from the sensingemployed, to control the relationship between W2 and L minus W2. Thus bysensing the count value at the input of delay device 110 a reducingsignal may be generated and control signals generated therefrom whichselect tappings in the delay devices 82 and 78 thereby altering therelative delays introduced by these two devices. If the total delay of78 and 82 is maintained constant, the trapezium or triangle will haveone height dimension which is perpendicular to the line scan directionbut if the total delay of 78 and 82 is also altered and for examplereduced on successive line scans, both sides of the trapezium ortriangle will be inclined to the perpendicular to the line scandirection.

We claim:

1. A method of analysing features in a field in which a video signalthereof is generated by line scanning, amplitude excursions relating tofeatures are detected by comparison with one or more reference voltagesand measurements are made on the detected signal pulses, comprising thefurther steps of, stretching each detected signal pulse by apredetermined amount to generate signals for each feature defining afirst capture zone, generating a control pulse upon detecting the end ofeach of said signals defining each first capture zone which does notcoincide with a detected signal pulse from another feature,recirculating the control pulse from line to line to define a secondcapture zone which extends in a direction generally perpendicular to thedirection of line scanning, and associating the detected signal pulsesfrom which capture zones are generated and which coincide with capturezones, thereby, to form an agglomerate.

2. A method as set forth in claim 1 further comprising the step ofterminating the control pulse defining the second capture zone on thelast line scan of the scan raster.

3. The method as set forth in claim 1 further comprising the step ofgenerating a cancel signal to terminate the control pulse defining asecond capture zone if coincidence is detected between signals definingthe second capture zone and detected signal pulses from another feature.

4. The method as set forth in claim 3 further comprising the step ofcancelling the control pulse defining a second capture zone after it hasbeen recirculated a predetermined number of times from line to line.

.5. The method as set forth in claim 3 further comprising the step ofrecirculating the control signal at precisely one line scan periodintervals.

6. The method as set forth in claim 3 further comprising the step ofrecirculating the control signal at intervals of less than one line scanperiod.

7. The method as set forth in claim 3 further comprising the step ofrecirculating the control signal at intervals of greater than one linescan period. I

8. The method as set forth in claim 3 further comprising the step'ofmaking measurements on the detected signal pulses relating to eachfeature, generating an information signal for each feature, accumulatingthe information signals arising from features within an agglomerate andreleasing the information signals by the output pulse generated upondetection of the end of the second capture zone of the last feature inthe agglomerate.v

9. The method as set forth in claim 8 further comprising the step ofmaking each information signal a count pulse so that the accumulatedinformation signal released at the end of an agglomerate constitutes thenumber of features within the agglomerate.

10. The method as set forth in claim 8 further comprising the step ofcombining with the information signal generated for each feature asignal proportional to the area of the feature whereby the accumulatedinformation signal released at the end of an agglomerate constitutes asignal proportional to the total of the individual areas of featureswithin the agglomerate.

11. The method as set forth in claim 8 further comprising the step ofgenerating the information signal for each feature proportional to alength dimension of the feature.

12. The method as set forth in claim 3 further comprising the step ofgenerating an output pulse upon detection of the end of a second capturezone if the signals defining the latter do not coincide with detectedsignal pulses relating to another feature.

13. The method as set forth in claim 12 further comprising the step ofcancelling the control pulse defining a second capture zone after it hasbeen recirculated a predetermined number of times from line to line.

14. The method as set forth in claim 13 further comprising the steps ofmaking measurements on the detected signal pulses relating to eachseparate feature, generating an information signal from saidmeasurements for each feature and releasing the information signal for afeature only if signals defining both first and second capture zonestherefor are not coincident with a detected signal pulse from anotherfeature.

15. The method as set forth in claim 14 further comprising the step ofselecting the information signal proportional to a length dimension ofthe feature measured perpendicular to the direction of line scan.

16. The method as set forth in claim 14 further comprising the step ofmaking the information signal proportional to a length dimension of thefeature measured in a direction parallel to the line scan direction.

17. The method as set forth in claim 14 further comprising the step ofutilizing the information signal for each feature as a count pulse.

18. The method as set forth in claim 17 further comprising the step ofcancelling the control pulse defining a second capture zone after it hasbeen recirculated a predetermined number of times from line to line.

19. The method as set forth in claim 18 further comprising the step ofmaintaining said predetermined number'constant for all features in afield.

20. The method as set forth in claim 18 further comprising the steps ofmaking the said predetermined number dependent on the value of theinformation signal generated for the feature.

21. The method as set forth in claim 20 further comprising the step ofselecting the information signal proportional to the area of thefeature.

22. Apparatus for analysing features in a field of which an image isscanned in a series of lines and a video signal is generated relatingthereto, comprising: threshold detector means for detecting amplitudeexcursions of the video signal relating to features, first circuit meanscoupled to said threshold detector means for stretching each detectedsignal pulse by a predetermined amount to generate for each feature afirst capture zone, second circuit means coupled to said thresholddetector means for associating detected signal pulses defining a firstcapture zone with those of a feature whose detected signal pulsescoincide therewith, third circuit means coupled to said thresholddetector means for generating a control pulse at the end of a firstcapture zone, means coupled to said third circuit means forrecirculating the control pulse from line to line to define a secondcapture zone which extends in a direction generally perpendicular to thedirection of line scanning, fourth circuit means coupled to said thirdcircuit means for detecting coincidence between a second capture zonesignal and a detected signal pulse from another feature for associatingdetected signal pulses from the said other feature with those of thefeature content generating the second capture zone.

23. Apparatus as set forth in claim 22 further comprising furthercircuit means for generating a cancel signal in the event thatcoincidence between a second capture zone signal and a detected signalpulse from another feature is detected and circuit means responsive to acancel signal to terminate the recirculation of the control pulsegenerating the said second capture zone. i

24. Apparatus as set forth in claim 23 further comprising circuit meansfor generating an output pulse at the end of a second capture zone ifcoincidence between a signal defining the latter and a detected signalpulse from another feature has not been detected.

25. Apparatus as set forth in claim 24 further comprising circuit meansfor terminating the recirculation of the control pulse after it has beenrecirculated a predetermined number of times from line to line.

1. A method of analysing features in a field in which a video signalthereof is generated by line scanning, amplitude excursions relating tofeatures are detected by comparison with one or more reference voltagesand measurements are made on the detected signal pulses, comprising thefurther steps of, stretching each detected signal pulse by apredetermined amount to generate signals for each feature defining afirst capture zone, generating a control pulse upon detecting the end ofeach of said signals defining each first capture zone which does notcoincide with a detected signal pulse from another feature,recirculating the control pulse from line to line to define a secondcapture zone which extends in a direction generally perpendicular to thedirection of line scanning, and associating the detected signal pulsesfrom which capture zones are generated and which coincide with capturezones, thereby, to form an agglomerate.
 2. A method as set forth inclaim 1 further comprising the step of terminating the control pulsedefining the second capture zone on the last line scan of the scanraster.
 3. The method as set forth in claim 1 further comprising thestep of generating a cancel signal to terminate the control pulsedefining a second capture zone if coincidence is detected betweensignals defining the second capture zone and detected signal pulses fromanother feature.
 4. The method as set forth in claim 3 furthercomprising the step of cancelling the control pulse defining a secondcapture zone after it has been recirculated a predetermined number oftimes from line to line.
 5. The method as set forth in claim 3 furthercomprising the step of recirculating the control signal at precisely oneline scan period intervals.
 6. The method as set forth in claim 3further comprising the step of recirculating the control signal atintervals of less than one line scan period.
 7. The method as set forthin claim 3 further comprising the step of recirculating the controlsignal at intervals of greater than one line scan period.
 8. The methodas set forth in claim 3 further comprising the step of makingmeasurements on the detected signal pulses relating to each feature,generating an information signal for each feature, accumulating theinformation signals arising from features within an agglomerate andreleasing the information signals by the output pulse generated upondetection of the end of the second capture zone of the last feature inthe agglomerate.
 9. The method as set forth in claim 8 furthercomprising the step of making each information signal a count pulse sothat the accumulated information signal released at the end of anagglomerate constitutes the number of features within the agglomerate.10. The method as set forth in claim 8 further comprising the step ofcombining with the information signal generated for each feature asignal proportional to the area of the feature whereby the accumulatedinformation signal released at the end of an agglomerate constitutes asignal proportional to the total of the individual areas of featureswithin the agglomerate.
 11. The method as set forth in claim 8 furthercomprising the step of generating the information signal for eachfeature proportional to a length dimension of the feature.
 12. Themethod as set forth in claim 3 further comprising the step of generatingan output pulse upon detection of the end of a second capture zone ifthe signals defining the latter do not coincide with detected signalpulses relating to another feature.
 13. The method as set forth in claim12 further comprising the step of cancelling the control pulse defininga second capture zone after it has been recirculated a predeterminednumber of times from line to line.
 14. The method as set forth in claim13 further comprising the steps of making measurements on the detectedsignal pulses relating to each separate feature, generating aninformation signal from said measurements for each feature and releasingthe information signal for a feature only if signals defining both firstand second capture zones therefor are not coincident with a detectedsignal pulse from another feature.
 15. The method as set forth in claim14 further comprising the step of selecting the information signalproportional to a length dimension of the feature measured perpendicularto the direction of line scan.
 16. The method as set forth in claim 14further comprising the step of making the information signalproportional to a length dimension of the feature measured in adirection parallel to the line scan direction.
 17. The method as setforth in claim 14 further comprising the step of utilizing theinformation signal for each feature as a count pulse.
 18. The method asset forth in claim 17 further comprising the step of cancelling thecontrol pulse defining a second capture zone after it has beenrecirculated a predetermined number of times from line to line.
 19. Themethod as set forth in claim 18 further comprising the step ofmaintaining said predetermined number constant for all features in afield.
 20. The method as set forth in claim 18 further comprising thesteps of making the said predetermined number dependent on the value ofthe information signal generated for the feature.
 21. The method as setforth in claim 20 further comprising the step of selecting theinformation signal proportional to the area of the feature. 22.Apparatus for analysing features in a field of which an image is scannedin a series of lines and a video signal is generated relating thereto,comprising: threshold detector means for detecting amplitude excursionsof the video signal relating to features, first circuit means coupled tosaid threshold detector means for stretching each detected signal pulseby a predetermined amount to generate for each feature a first capturezone, second circuit means coupled to said threshold detector means forassociating detected signal pulses defining a first capture zone withthose of a feature whose detected signal pulses coincide therewith,third circuit means coupled to said threshold detector means forgenerating a control pulse at the end of a first capture zone, meanscoupled to said third circuit means for recirculating the control pulsefrom line to line to define a second capture zone which extends in adirection generally perpendicular to the direction of line scanning,fourth circuit means coupled to said thiRd circuit means for detectingcoincidence between a second capture zone signal and a detected signalpulse from another feature for associating detected signal pulses fromthe said other feature with those of the feature content generating thesecond capture zone.
 23. Apparatus as set forth in claim 22 furthercomprising further circuit means for generating a cancel signal in theevent that coincidence between a second capture zone signal and adetected signal pulse from another feature is detected and circuit meansresponsive to a cancel signal to terminate the recirculation of thecontrol pulse generating the said second capture zone.
 24. Apparatus asset forth in claim 23 further comprising circuit means for generating anoutput pulse at the end of a second capture zone if coincidence betweena signal defining the latter and a detected signal pulse from anotherfeature has not been detected.
 25. Apparatus as set forth in claim 24further comprising circuit means for terminating the recirculation ofthe control pulse after it has been recirculated a predetermined numberof times from line to line.